The invention relates to constructive improvements in a film folding and supplying unit for the machines described in the Italian patent n. 1 266 296, property of the same applicant, to which is made wide reference. In this type of machines, the packaging film has a width which is suitable for the packaging of products which have variable dimensions inside a large range and its width is proportionate to that of the products having the greatest dimension that the machine can wrap. The width of the film is adapted to the dimensions of the product to be wrapped, with a process of pleating of the same film during the feeding phase to the wrapping phase, so that the longitudinal axis of the pleats which are oriented in the length direction of the portion of film inserted in said station and such that in the packaging of products having small dimensions, it is in any case provided for the formation of a wrapping which is enough wrapped and blocked. In this type of machines, the film is unwound from the feeding bobbin, passes through the tightening pulley which provides a longitudinal tensioned feeding and then is transmitted on a transversal and arched roller which transversally tensions the same and avoid the formation of uncontrolled pleats because the film is coming out from said roller with an ascending direction and runs longitudinally with its own center portion, on a rectilinear guide anteriorly provided with an idle roller which facilitates the entry of the film the lateral edges of which are folded under said guide by means of respective lateral guides, the whole in such a manner that the film is folded with a pressed omega transversal shape, and presents in such manner a width which is proportionate to the width of the product to be wound. Said curved transmission roller has been resulted of difficult realization so that it has been thought to substitute the same with a composite roller formed by a central roller and two long lateral rollers, having the same distance from the central roller with an angle of about 170° Another drawback found in the apparatus of the known type, is due to the great contact surface of the film with the folding guides above mentioned which were realized with polished metal or with material having a low friction coefficient. To improve the folding action performed by the guides, the same have been provided on the edges which was before operating in contact with the film, with rows of idle wheels with which the film is co-operating with rolling friction.
The lateral edges of the film which is coming out from said folding which are external to the folded portion of the said film, run upon rubber and idle rollers upon which the same are maintained in contact by a contrast superior roller, idle, but made of metal and sprung, after that the folded film arrives to a gripper-shaped distributor, made by a lower fixed portion, to which there is fixed in projecting manner said longitudinal and central guide, and by an upper portion assembled upon a structure which may oscillates upon an anterior axis which is parallel to the same distributor, and which is carrying the final folder of the machine, the one which is folding on the bottom of the product the last portion of film previously retained by the same distributor, and which is carrying the heated conveyor for the welding of the lower edges of the packaging. This structure may be raised with oscillation upon said transversal axis, in the initial phase in which the film coming from a new bobbin must be inserted in a machine. Upon this structure there is assembled said metallic and sprung roller which co-operates with said rubberized rollers. The distributor of the film realized with the known technique, is complex and scarcely reliable. An object of the invention is to improve the distributor and to provide freewheel means in the upper metallic roller contrasting the rubberized rollers, in such a manner that the film which passes through said rollers may only go forward and not backward.
In the apparatus of the described type, both folding guides of the lateral edges of the film fed by the machine, and the rubberized rollers, are pre-arranged to be automatically adjustable in the reciprocal distance by means of self-centering regulation mechanism, controlled by an electric step motor controlled by the computer of the machine which by means of the optical barriers detects the dimensions of the products to be packaged, to automatically adjust to these the width of the packaging film.